How to define and access a list property for a game object in BGE
You will have to define the list in the script like this:

if 'list' not in object:
    object['list'] = []


You can then add objects using functions such as

object['list'].append('x') # adds the string 'x' to the end
object['list'].instert(3, 'x') # adds the string 'x' at position 3